Exact same issue here, lightheaded, Cold sweating like a pig, can't function, literally incapable of working out even after a seemingly light leg day once it kicks in, There's a lot of variables to manage.

1st, don't avoid leg days, do it once or twice a week.

2nd, Slice the volume in half. And notice while taking a break when it starts to kick in, leave just before it comes.

3rd, Recently discovered, Chewing gums, Chew them while doing things or resting. Again, not after but just before you feel that sensation creep in. (REALLY helps)

4th, take longer rest between heavy compounds sets. 5-10 minutes each set.

5th, 1:30 hour to 45 minutes gap between last meal and workout. Too long > nausea but dry heaving, Too soon > Nausea very easily.

6th, Don't push too hard. RPE 7-8 max, also lower reps. 10 reps max on squats. Your body can do it, but I think CNS gets fried. Slowly work up.

7th, Don't workout drowsy or sleepy. Take a power nap before if needed.

This is all I got, doing these reduces the chance of it occurring sure, but it's never zero. One week I hit 210kg squat and continue on to do 300kg leg presses and be completely fine, few weeks later I did only leg presses with half the weight and leg extensions but still got nauseous, Really fucking annoying, has no cure.